Apparatus for driving tunnels



Aug. 29, 1961 PER APPARATUS FOR DRIVING TUNNELS 4 Sheets-Sheet 1 FiledJuly 14. 1958 T [H l INVENTOR.

\ V Mam/44 EKZMpA-e MQQ/W Aug. 29, 1961 M. F KEMPER APPARATUS FORDRIVING TUNNELS 4 Sheets-Sheet 2 Filed July 14. 1958 Q INVENTOR Aug. 29,1961 M. F. KEMPER APPARATUS FOR DRIVING TUNNEILS Filed July 14. 1958 1%.6'. I H 44 I i 47 i 46 law i t i i 40 151 0 4/ g i 1 as 42 I g 59IILJVENQTOR. -*1 MIN/[ll If 1514714256 4 Sheets-Sheet 3 A 29, 1961 M. F.KEMPER APPARATUS FOR DRIVING TUNNELS 4 Sheets-Sheet 4 Filed July 14.1958 INVENTOR. Mwwzz; .lffi

EMPEE U ted. St tes Patent 2,997,853 APPARATUS FOR DRIVING TUNNELSMaxwell F. Kemper, 3701 Overland, Los Angeles 34, Calif. Filed July 14,1958, Ser. No. 748,340 8 Claims. (Cl. 61--85) The present inventionrelates to novel apparatus for driving a tunnel through earth formationwhile supporting the overburden to prevent cave-in thereof.

In my copending application, Serial No. 678,993, there is disclosed anovel method and apparatus for driving tunnels through earth formationwhich contemplates a substantial advance in the art of forming tunnels,particularly in sandy soils where previously it had been the practice toprovide an outside form for forming a concrete storm sewer or drain bysuccessively supporting arched or horseshoe shaped beams or steelsupports in spaced relation longitudinally of a tunnel as the tunnelprogressed.

The method and apparatus of that application substantially facilitatesthe formation of such an outer form and materially lessens the need formanpower while at the same time speeding up the operation. Thatinvention contemplated the utilization of a shell of generally horseshoecross section which was adapted to be driven forcefully in the face ofthe tunnel as the tunnel pro- 'gressed, so as to enable erection ofsuitable supporting structure within the protective cover of the shell.For supporting the shell, in accordance with my earlier invention anovel needle beam support was centrally located within the shell so asto support the latter as it was advanced into the tunnel face andprevent the overburden of earth above the shell from forcing the latterdownwardly.

Though not limited thereto, the apparatus of my earlier invention isparticularly adapted for use in forming tunnels for comparatively largestorm drains or the like, where space limitation for the operation ofauxiliary equipment and appliances within the shell during formation ofthe tunnel is not of particular moment.

The present invention contemplates an improved tunnel driving shellsupport in the sense that improved shell supporting means are providedwhereby maximum head room and transverse clearance are made availablefor the use of such auxiliary equipment as mucking machines and thelike, as would particularly be necessary and desirable when smallertunnels are being formed.

Accordingly, a principal object of the invention is to provide novelsupporting means for the shell of tunnel driving apparatus of the typebroadly contemplated in my copending application previously referred to.In accomplishing this objective, a pair of supporting jacks areprovided, these jacks being transversely spaced within the tunneldriving shell, so as to provide a maximum of transverse spacetherebetween. These side jacks are adapted to remain stationary as theshield is being fed axially'into the face of the tunnel relativethereto. In addition, a central ormiddle jack is provided for supportingthe shield as the side jacks are alternately shifted to new positionsfor supporting the shield as it is being advanced. When the central jackis elevated to an inoperative position as the shield is being moved intothe tunnel face, the central jack occupies a minimum of space andthereby affords the maximum head room or clearance for the operation ofsuch equipment as frontloading overhead-unloading mucking machines whichare employed to load a conveyor or the like for removing earth from theface of the tunnel as the tunnel progresses.

Other objects and advantages of the invention will hereinafter bedescribed or will become apparent to those Pate nted Aug. 29, 1961 iceskilled in the art and novel features of the invention will be definedin the appended claims.

In the accompanying drawings:

FIG. 1 is a longitudinal sectional view taken through tunnel drivingapparatus made in accordance with the invention with the shield disposedfor movement into the face of the tunnel relative to the side jacks andwith the central jack partially elevated to an out-of-the-way position;

FIG. 2 is a view similar to FIG. 1 but showing the shield in theposition which it occupies after having been projected a full stroke andshowing the central jack in a shield supporting position with one of theside jacks in an inoperative position and ready to be advanced to a newshield supporting position;

FIG. 3 is a transverse sectional view as taken on the line 3-3 of FIG.1, but showing the central jack prior to its elevation to a horizontalposition, and also depicting steel support jacks which are employed forjacking the horse-shoe shaped steel supports 'or supporting ribs intoplace;

FIG. 4 is a front elevational view showing the apparatus substantiallyin the same condition as shown in FIG. 1;

FIG. 5 is a fragmentary detail view partly in elevation and partlybroken away and shown in section depicting one of the jacks;

FIG. 6 is a fragmentary view in elevation and on an enlarged scale,showing a novel roller support for one of the side jacks;

FIG. 7 is a view partly in elevation and partly in section as takensubstantially on the line 77 of FIG. 6;

FIG. 8 is a fragmentary detail view on an enlarged scale, showing thenovel connection of the central jack to the shield frame;

FIG. 9 is a View as taken substantially on the line 99 of FIG. 8; and

FIG. 10 is a fragmentary view on an enlarged scale depicting the centraljack hoist mechanism for elevating the central jack to a horizontalposition.

Like reference characters on the several figures of the drawings and inthe following description designate corresponding parts.

In accordance with the invention, the apparatus comprises a generallyU-shaped shield S having an outer skin plate 1 providing an elongatedskirt 2. Extending inwardly from the skin plate 1 are a suitable numberof longitudinally spaced plates 3, which are welded or otherwisesuitably secured to the skin plate '1 and at their inner margins areprovided with ribs 4. Gussets 5 are welded into the angle formed at theforemost structural plate 3 and the forward end of the shield S, whichis at the left hand end of the shield as viewed in FIG. 1. On thelongitudinal center of the shield S there is an assembly providingsupporting rail means 6, which, as best seen in FIG. 9, comprises a pairof vertical, laterally spaced plates 7 and 8, which are interconnectedat their base by means of a rail 9 adapted to shiftably support thecentral jack assembly 10. At opposite sides of the rail assembly 6 theshield is also provided with vertically disposed rail assemblies 11 and12, respectively, which, as best seen in FIG. 7, also comprise a pair ofvertically disposed plates .13 and 14 interconnected by a rail 15 whichis adapted to support one of a pair of side or operating support jacks16, 16. Extending axially through a number of the rearmost structuralplates 3, is a suitable number of generally equi-distantly spaced rams17, having rearwardly extending pistons 18. These rams 17 serve thepurpose of propelling the shield into the face of the tunnel asgenerally designated at F.

Since tunnels are ordinarily driven into rather sandy soils when theshields of the type concerned are employed,

means are also preferably provided for supporting the tunnel face, andin the illustrative embodiment a plurality of air operated rams 19,having pistons or rods 20, are disposed in spaced relation about theshield and are provided with breastboard supporting brackets 21 at theirouter extremities for supporting breastboards 22. Inasmuch as the rams19 are air operated, air therein will form a resilient cushion enablingthe rods or pistons to be pushed back into the rams as the shieldadvances, while the breastboards 22 will be held out firmly against thetunnel face F, thus preventing cave-in.

In forming a tunnel into earth formation, FIG. 1 illustrates the shieldinv a tunnel which has been partially formed, where it will be seen thata series of generally horseshoe shaped H beams or steel supports 23 havebeen mounted in place with lagging strips 24 installed between the steelsupports 23 and the skirt 2 of the shield S and as the shield progressesaxially into the face of the tunnel, the lagging is uncovered andconstitutes the outer form for a concrete conduit to .be constructed inthe tunnel. However, it will be understood that for some applicationssuch as mining or the like it may be desirable to construct the steelsupported wooden frame for containing the earth in a mine tunnel. Forthe purpose of description it will be assumed that the steel supportdesignated 23a has been firmly installed.

This is accomplished by means of a pair of manual jacks or the like (seeFIG. 3), which are employed, following installation of the laggingbetween the steel support 23a and the next adjacent steel 23, to jackthe steel 23a firmly toward the shell or skirt 2, whereupon a base plate26 may be installed beneath the opposite lower extremities of the steelsupport 23a to prevent its settling upon release of the jacks 25.

Elevating means generally designated 27, which will hereinafter be moreparticularly described, are employed to elevate the central jack 10 froma vertical position as shown in FIG. 3, to the horizontal position asshown in FIG. 1. With the shield in the condition shown in FIG. 1,hydraulic fluid under pressure may be admitted to the rams 17, thusforcing the pistons 18 therefrom. These pistons are engaged with thesteel support 23a which is firmly backed up by collar braces 30, thelatter being interposed between the respective steel supports or ribs23.

Fluid under pressure may be admitted to the rams 17 by means of thehydraulic system disclosed and claimed in my copending patentapplication referred to above, or if desired other fluid pressureoperating systems may be employed. In any event, fluid under pressure inthe rams 17 will force the pistons 18 therefrom, which will effect axialmovement of the shield S into the face of the tunnel until the shieldreaches a position such as that shown in FIG. 2, With the pistons 18 oframs 17 fully extended. Whereupon, the central jack 10 will be loweredto the position shown in FIG. 2 and operated so as to partially supportthe shield S at which time an additional shield support 23 and lagging24 may be installed. As the shield S is advanced, the earth at thetunnel face F may be removed by mucking equipment (not shown), as moreparticularly described in my abovementioned copending application, butthe breastboards 22 will prevent the face of the tunnel from falling inwhile the rams 19 permit the shield to move relative to the rods orpistons 20, as air in the rams 19 is compressed. These rams 19 may alsobe operated by means of the pneumatic system disclosed in my copendingapplication above referred to, or if desired the rams 18 may be purelyspring loaded or other pneumatic operating systems may be employed.During the advance of the shield S into the tunnel roller supportassemblies generally designated 31, and more particularly shown indetail in FIGS. 6 and 7, will permit the shield to move axially upon theside jacks 16, which will be firmly based upon the tunnel floor, asillustrated in FIGS. 1, 3 and 4.

In order to stabilize the side jacks 16, they are preferably tied as bymeans of a line 33 provided with a hook 34 for engagement with theroller support 31, and engaged at its other end with a come-along 35,which in turn is securely connected as at 36 to a previously installedsteel support 23. Such an arrangement is employed with each of the sidejacks 16 so that they are firmly held against any tendency to move alongwith the shield S as it is urged into the tunnel face by the rams 17.Following movement of the shield S from the position shown in FIG. 1 tothe position shown in FIG. 2, and following the installation of lagging24 and an additional steel support 23, the central jack 10 will beretracted by means presently to be described, and elevated by themechanism 27 to a position extending substantially horizontally anddisposed closely adjacent to the rail 9. However, prior to retractingand elevating the central jack 10, the side jacks 16 will have beenshifted forwardly to the position shown in FIG. 1. One of the jackmechanisms is more particularly shown in detail in FIG. 5, and thestructure illustrated in FIG. 5 is representative of each of the jacks16 as well as the central jack 10.

Referring particularly to FIG. 5, which is representative of the jacks10 and 16, it will be noted that the jacks comprise an upper cylindricalhousing or body 38, which is relatively stationary and an internalcylindrical member 39 which is movable axially in the body 38. At itsupper extremity the cylindrical member 39 is provided with a closure 40through which extends a rod 41 having at its lower extremity a springseat 42 interposed between the closure or head 40 of the member 39 andthe seat 42, and disposed about the rod 41, is a return spring 43. Atits upper extremity the rod 41 is secured in any suitable manner to afixed head 44, which in turn is securely mounted within the cylindricalbody 38 in sealed relation thereto. Mounted externally of the body 38 isa hand pump 45 adapted to supply hydraulic fluid through a line 46 to ajack pressure chamber 47 whereby manipulation of the pump 45 willpressurize the chamber 47, thus acting upon the head 40 of the member 39to shift the same downwardly and compress the spring 43 between the head40 and the seat 42. Any of the jacks 10 and 16 may be operated in theforegoing manner so as to exert the strong vertical force tending tosupport the overburden of earth on the shield S as the shield is beingshifted into the tunnel face, or as the jacks 16 are being shifted fromthe position shown in FIG. 2 to the position shown in FIG. 1 inpreparation for a further advance of the shield.

During movement of the shield S into the tunnel, as has been previouslypointed out, the shield is shiftably supported upon the side jacks 16 bymeans of the roller supports 31. Referring more particularly to FIGS. 6and 7, the details of a representative roller support are moreparticularly shown. Upstanding from the upper extremity of therespective side supports 16 is a pair of spaced supporting ears 50through which is extended a pivot pin 51. The pivot pin 51 is journalledin the central body section of a supporting frame having opposed sidewalls 52 interconnected by transversely extended plates 53 at theopposite ends of the side walls. The pivot pin 51 extends through theside walls and is retained in place as by collars 54 and pins 55 whichextend through the collars 54 and thence through the pivot pins 51, sothat the respective side supports 16 are freely pivotally mounted on theside walls 52 of the roller supports 31.

Adjacent the opposite ends of the respective side walls 52 of eachroller support 31, is an internal roller 56, and as best illustrated inFIG. 7, each roller 56 is journalled upon a bushing 57 surrounding aretainer pin or axle 58, having a stem extending through an opening inthe side wall 52 and secured therein as by welding at 59. Preferably theretainer pin 58 is provided with a lubricant passage 60 for enablinglubrication of the bushing 57. Thus it is seen that opposed pairs of therollers 56 project laterally inwardly towards the vertical plates13 and14 upon which is secured the horizontal rail 15. The rollers 56 overliethe outwardly projecting edges of the rail 15 so as to hang the rollersupport 31 thereon. These rollers 56, it will be understood, are notrequired to support loads during use of the invention but instead aremerely required to sustain the weight of the respective side supports 16when they are disengaged from the floor of the tunnel.

Load bearing rollers 61 are disposed beneath the rail 15 at oppositesides of the pivotal center of the roller support 31. The rollers 61 arepreferably flanged so as to straddle the rail 15 as clearly indicated inFIG. 7, and each roller 61 is journalled upon a pin or axle 62 extendingtransversely between the side walls 52-52 of the roller support 31 witha bronze or other bushing 63 interposed between the roller and the pin62. Collars 64 are disposed about the opposite extremities of the pins62 and are welded to the side walls 52 as at 65, while the pins 62 aresecured to the collars 64 as by means of a pin 66. In addition, each pin62 is also provided with a lubricant passage 67 and a grease fitting 68for each roller 61, to enable lubrication of the rollers which should bemaintained well lubricated in view of the heavy loads imposed thereon asthe shield is progressing into the tunnel. The means for supporting thecenter support or jack on the rail 9 of the supporting rail means 6 ismore particularly illustrated in FIGS. 8 and 9. A pair of de pendingbrackets 70 interconnected beneath the rail 9 by a horizontal plate 71,are adapted to be adjustably connected to the rail by means of setscrews 72 which extend through the brackets 70 into overlying relationto the rail 9 and into engagement with the rail supporting plates 7 and8. The set screws 72 are threaded in nuts 73, which are preferablywelded to the brackets 70. Center jack 10 is pivotally disposed betweenthe brackets 70 as by means of a pivot pin or bolt 74, so that the jack10 may be swung from a substantially horizontal position as shown inFIG. 1, and as shown in broken lines in FIG. 8, to the verticalposition, as shown in FIGS. 2, 3, 8 and 9. At the upper extremity of thejack 10, it is provided with a pair of upstanding arcuate plates 75,which when the jack '10 is disposed in a vertical position, bear beneaththe horizontal plate 71 at points vertically beneath the rail supportingplates 7 and 8. Thus the load of the shield S is not borne upon the,jack supporting means when the side jacks 16 are disengaged from thetunnel floor, but instead the load is borne directly through the rail 9,horizontal plate 71, and arcuate brackets 75.

In order to swing the central support jack 10 from a vertical positionto a horizontal position, a flexible chain 76 is connected to the jack10 and is threaded over a sheave 77 ot the elevating means, which isgenerally designated 27, and which has been previously referred to. Asshown in FIG. 1, sheave 77 is supported on a bracket 78 secured beneaththe center rail 9 at a point spaced forwardly from the rearwardextremity of the rail 9. Adjacent the rear extremity of the rail 9 is asheave support 79 having a pair of transversely spaced sheaves 80 and 81carried thereby and rotatable upon vertical axes. The chain or cable 76is passed from sheave 77 over sheave 80 and thence over sheave 81, firomwhence it extends longitudinally in parallel relation to the rail 9 andthence, as best seen in FIG. 10, over a guide sprocket 82, and a drivesprocket 83 of an air or other suitably powered motor 84 mounted as at85 upon skin plate 1. Any suitable means may be employed for poweringthe motor 84 so as to feed the chain 76 in a direction to allow thecenter jack 10 to gravitate to an upstanding position or to retrieve thechain 76 so as to elevate the jack 10 as will now be apparent.

In the use of the shield of the present invention after a tlmnel hasbeen commenced, such as by appropriately backing up the shieldexteriorly of the tunnel entrance 6 and oommencingthe'progressiveadvancing of the shield and installation of lagging and steel supports,the operation is substantially as follows. Referring to FIG. 1, theshield is in condition for being advanced into the tunnel face F, andthe breast boards 22 will eifectively preclude cave-in of the tunnelface.

The application of power fluid from a suitable source to the rams 17will force the shield S into the tunnel face as the shield is supportedupon the side jacks 16 and moves relatively easily thereon upon theroller supports 31. When the shield rams 17 have been fully extended, asfor example as shown in FIG. 2, the center jack 10 will be lowered bythe motor 84 and an additional generally horsehoe-shaped steel support23 will be installed in spaced relation to the last installed steelsupport. Before jacking up the newly installed steel support into finalposition, lagging 24' will be installed between the newly located steelsupport and the steel support last installed following which the jacks25 will be employed to jack the steel support into firm engagement withthe lagging and press the latter into supporting engagement with theinner surface of the skirt 2 of the shell S. A base plate 26 will bedisposed beneath the newly installed steel support 23, following whichthe jacks 25 will be removed. Whereupo'n, with the shell rigidlysupported upon the center jack 10,-the side support jacks may beelevated and shifted to their forward position, as shown in FIG. 1, fromtheir rearward position as shown in FIG. 2, and then repressurized tosustain the load of the shell. At this time the center jack 10 willagain be elevated to a horizontal position for reco'mmencement of theshifting cycle.

It should be observed that with the center jack 10 ele vated to anout-of-the-way position, and with the shell supported upon the side jaclcs 16, a maximum of headroom is provided, and in addition the sidejacks 16 are disposed in laterally spaced relation to the greatestextent possible for enabling freedom of movement of mucking equipment orother apparatus as well as the crewmen working at the tunnel face.

While the specific details of the invention have been herein shown anddescribed, changes and alterations may be resorted to without departingfrom the spirit thereof as defined in the appended claims.

I claim:

1. Apparatus for digging a tunnel in the earth comprising: a generallyhorseshoe shaped elongated shield; means shiftably supporting saidshield for axial mo'vement; and means for advancing said shield; saidsupporting means including a pair of longitudinally extended memberscarried by said shield adjacent the top of said shield and disposed inlaterally opposed transversely spaced relation at opposite sides of thelongitudinal center or said shield; a pair of extensible jacks disposedin spaced relation transversely of said shield; means operativelyconnecting the respective jacks to said members for permitting relativelongitudinal movement of said shield and said jacks; said supportingmeans for each of said jacks including a track extending longitudinallyof the shield; and a roller support shi'fitably carried by said trackand operatively connecting its jack to said track.

2. Apparatus as claimed in claim 1, said supporting means for each ofsaid jacks including a track extending longitudinally of the shield; anda roller support shiftably carried by said track and operativelyconnecting its jack to said track; said track having free lateral edges;and said roller support having rollers disposed above and below saidlateral edges.

3. Apparatus as defined in claim 1, wherein the sup porting means foreach of said jacks including a track extending longitudinally of theshield; and a roller support shittably carried by said track andoperatively connecting its jack to said track; said roller supporthaving side walls disposed at opposite sides of said track; a loadsupporting roller disposed beneath said track and extending between saidside walls; and a jack supporting roller 7 disposed above said track andcarried by one of said side walls.

4. Apparatus for digging a tunnel in the earth comprising: a generallyhorseshoe-shaped elongated shield; means shiftably supporting saidshield for axial movement; and means for advancing said shield; saidsupporting means including a pair of longitudinally extended memberscarried by said shield adjacent the top of said shield and disposed inlaterally opposed transversely spaced relation at opposite sides of thelongitudinal center of said shield; a pair of extensible jacks disposedin spaced relation transversely of said shield; means operativelyconnecting the respective jacks to said members for permitting relativelongitudinal movement of said shield and said jacks; said supportingmeans for each of said jacks including a track extending longitudinallyof the shield; and a roller support shiftably carried by said track;said shield having means supporting said track thereon; and said trackprojecting laterally from said supporting means; said roller supporthaving rollers disposed on said track at opposite sides of saidsupporting means and engaging said laterally projecting track to supportsaid jack; and a roller disposed beneath said track for supporting saidshield.

5. Apparatus for digging a tunnel in the earth comprising: a generallyhorseshoe-shaped elongated shield; means shiftably supporting saidshield for axial movement; means for advancing said shield; saidsupporting means including a pair of extensible jacks disposed in spacedrelation transversely of said shield; and means connecting therespective jacks to said shield and providing for relative longitudinalshifting movement of said shield and said jacks; wherein the supportingmeans for each of said jacks including a track extending longitudinallyof the shield; and a roller support shiftably carried by said track;said roller support having opposed side walls; a pivot pin extendingbetween said side walls; said jack being pivotally mounted on said pin;a pair of load sustaining rollers disposed on opposite sides of saidpivot pin and journalled in said side walls; said rollers being engagedbeneath said track; and means carried by said side walls and engagedwith the top of said track for supporting said jack on said track.

6. Apparatus for digging a tunnel in the earth comprising: a generallyhorseshoeashaped elongated shield; means shiftably supporting saidshield for axial movement including a pair of vertically disposedmembers disposed at opposite sides of the longitudinal center of saidshield and operatively engaged with said shield adjacent the top of thelatter; means for advancing said shield; said supporting means includingmeans operatively connecting said supporting means to said shield fo'rrelative longitudinal shifting of said shield and said supporting means;and means for supporting said shield while said supporting means arebeing shifted, including a centrally disposed jack; means pivotallyconnecting said centrally disposed jack to said shield; said connectingmeans including a track extending longitudinally of said shield at thelongitudinal center of the shield; and means adjustably mounting saidjack on said track for movement longitudinally of said track.

7. Apparatus for digging a tunnel into the earth comprising: a generallyhorseshoe-shaped shield having an elongated skirt; and means foradvancing said shield into the tunnel face; said shield having laterallyopposed vertical plates depending therefrom and extending longitudinallyof the shield adjacent the top of the shield in transversely spacedrelation at opposite sides of the longitudinal center of said shield;shield supporting jacks shiftably carried by said plates so as to permitrelative longitudinal shifting of said shield and said jacks; and acentral jack carried by said shield; means pivotally connecting saidsupporting jacks to said plates including roller supports 'operativelyconnecting said jacks and said plates for longitudinal movement of saidjacks; and means pivotally connecting said central jack to said shield.

8. Apparatus as defined in claim 7 wherein each of said jacks isextensible by fluid pressure and including means for supplying fluidunder pressure to said jacks; each jack includingmeans for resilientlyretracting said iacks.

References Cited in the file of this patent UNITED STATES PATENTS498,855 Morris June 6, 1893 1,275,910 Hamilton Aug. 13, 1918 1,478,163Anderson Dec. 18, 1923 1,751,147 Hackley Mar. 18, 1930 2,196,100 OaputoApr. 2, 1940 2,757,515 Wilbur et a1. Aug. 7, 1956 FOREIGN PATENTS567,122 Germany Dec. 28, 1932 816,539 Germany Oct. 11, 1951 911,961Germany May 24, 1954 773,407 Great Britain Apr. 24, 1957 UNITED STATESPATENT OFFICE CERTIFICATION OF CORRECTION Patent No. 2397.853 August 29,1961 Maxwell F. Kemper It is hereby certified that error appears in theabove numbered patent requiring correction and that the said LettersPatent should read as corrected below.

Column 6, line 61, strike out "Apparatus as claimed in claim 1," and inline 63, strike out "Apparatus as defined in claim 1, wherein" andinsert instead in each occurrence, the following:

Apparatus for digging a tunnel in the earth comprising: a generallyhorseshoeshaped elongated shield; means shiftably supporting said shieldfor axial movement; and means for advancing said shield; said supportingmeans including a pair of longitudinally extended members carried bysaid shield adjacent the top of said shield and disposed in laterallyopposed transversely spaced relation at opposite sides of thelongitudinal center of said shield; a pair of extensible jacks disposedin spaced relation transversely of said shield; means .operativelyconnecting the respective jacks to said members for permitting relativelongitudinal movement of said shield and said jacks;

Signed and sealed this 27th day of February 1962..

(SEAL) Attest:

ERNEST We SWIDER DAVID L.. LADD Attesting Officer Commissioner ofPatents

